Method of making a fluoride functionalized zeolite catalyst and method of use

ABSTRACT

A method for producing a fluoride functionalized zeolite catalyst is described, having a F/Si molar ratio of 0.1:1-3:1. The method involves mixing a fluoride salt with zeolite components to form a gel, which is then hydrothermally treated and calcined. The fluoride functionalized zeolite catalyst may be used for cracking an olefin stream into ethylene, propylene, and butylene, with high selectivity towards propylene. The fluoride functionalized zeolite catalyst may be used for 50 or more hours with a stable conversion rate and low coke formation.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a method of making a fluoridefunctionalized zeolite catalyst and a method of using a fluoridefunctionalized zeolite catalyst to catalytically crack an olefin streaminto lighter hydrocarbon products.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Propylene and ethylene are crucial components in the petrochemicalindustry to produce many chemical intermediates and polymers such aspolypropylene, oxo alcohols, propylene oxide, cumene, methylmethacrylate, phenol, acrylic acid, isopropyl alcohol, acrylonitrile,oligomers, and other miscellaneous intermediates. The main source ofpropylene production in the petrochemical industry is as a byproductfrom fluid catalytic cracking (FCC) units or as the product fromprocessing ethane and heavier feedstocks in steam crackers. The amountof propylene coproduced in a steam cracker depends mostly on the natureof the feedstock. However, with the recent sharp decline in oil prices,the cost advantage of ethane cracking has diminished, and crackeroperators are likely to crack heavier feeds and produce more propylene.This scenario may be changed once again with an increase in oil prices.Based on the ethylene and propylene market price fluctuations, the P/E(propylene/ethylene) ratio plays an important factor in catalyticcracking of olefins. Commercially, Olefin Cracking Process(UOP-ATOFINA), Propylur (Lurgi), PCC process (Exxon-Mobil), SUPERFLEX®(Lyondell/Kellogg) and Mobil's Olefin Interconversion Process (MOI) areavailable for production of lower olefins such as ethylene and propyleneusing C₄-C₅ streams. Cracking of C₄-C₆ alkenes appears to be a promisingroute for the production of propylene and ethylene.

Nawaz et al. showed the role of bulk topology/structure of SAPO-34catalysts using 1-hexene catalytic cracking. However, the catalystdeactivation rate was much faster when compared to ZSM-5 catalysts. SeeNawaz, Z. et al. Chin J Catal, 30 (2009) 1049-1057—incorporated hereinby reference in its entirety

Buchanan et al. showed higher propylene selectivity (83%) with lower1-hexene conversion (66%) using ZSM-5 with a Si/Al₂ ratio of 650 at 510°C. and with a 10 Torr partial pressure. See Buchanan et al. J.Catalysis, 158 (1996) 279-287—incorporated herein by reference in itsentirety.

Koyama et al. studied the effect of pore volume on propylene selectivityin 1-hexene cracking using ZSM-22 as catalyst. The selectivity forpropylene gradually decreased from 93% to 80% with increasing conversionof 1-hexene from about 1 to 80%. However, the stability of the catalystwas not reported. See Koyama et al. Phys. Chem. Chem. Phys., 12 (2010)2541-2554—incorporated herein by reference in its entirety.

Yuxiang Liu et al. showed the role of fluoride ion in the synthesis ofSAPO-11. The fluoride ion inhibits coke deposition by suppressingcondensation reactions. See Liu, Yuxiang et al. Microporous andMesoporous Materials 198 (2014) 230-235—incorporated herein by referencein its entirety.

The foregoing discussions show that there has been no report availablein effect of fluoride ion in synthesis of ZSM-5 catalyst to enhance thecatalytic cracking of higher olefins to propylene and ethylene.

In view of the foregoing, one objective of the present invention is toprovide a method of making a fluoride functionalized zeolite catalyst,and a method of using a fluoride functionalized zeolite catalyst forcracking a C₄-C₆ olefin into ethylene, propylene, and/or butylene.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to a methodfor producing a fluoride functionalized zeolite catalyst. The methodinvolves the step of mixing a structure directing agent, an inorganicfluoride salt, an aluminum salt, a silicating agent, and water to form agel, where the gel has a F to Si molar ratio of 0.1:1.0-3.0:1.0. Themethod involves the step of heating the gel at 180-250° C. for 12-72 hto produce a crystallized product, and calcining the crystallizedproduct in air at 600-850° C. for 3-12 h to produce the fluoridefunctionalized zeolite catalyst.

In one embodiment, the structure directing agent is a quaternaryammonium salt with a chemical formula N(C_(n)H_(3n))₄ ⁺X⁻. X is a halideion or a hydroxide, and n is an integer from 1 to 5.

In one embodiment, the inorganic fluoride salt is ammonium fluoride.

In one embodiment, the gel and the fluoride functionalized zeolitecatalyst are substantially free of phosphorous and sodium.

In one embodiment, the aluminum salt is aluminum nitrate or aluminumsulfate.

In one embodiment, the fluoride functionalized zeolite catalyst has a Sito Al molar ratio of 500:1-2,000:1.

In one embodiment, the fluoride functionalized zeolite catalyst has anaverage crystal size of 0.1-50 μm.

In one embodiment, the fluoride functionalized zeolite catalyst has atotal acidity of 0.017-0.020 mmol/g as defined by NH₃-TPD.

In one embodiment, the silicating agent is at least one selected fromthe group consisting of tetraethylorthosilicate,tetramethylorthosilicate, silica, and polydimethylsiloxane.

In one embodiment, the fluoride functionalized zeolite catalyst is aZSM-5 type zeolite.

In one embodiment, the fluoride functionalized zeolite catalyst has asurface area of 330-400 m²/g.

According to a second aspect, the present disclosure relates to afluoride functionalized zeolite catalyst produced by the method of thefirst aspect.

According to a third aspect, the present disclosure relates to a methodof using a fluoride functionalized zeolite catalyst to convert a C₄-C₆olefin into ethylene, propylene, and/or butylene. The method involvescontacting a gas stream comprising the C₄-C₆ olefin with the fluoridefunctionalized zeolite catalyst at a temperature of 400-700° C. toproduce ethylene, propylene, and/or butylene. Here, the fluoridefunctionalized zeolite catalyst has a F to Si molar ratio of0.1:1.0-3.0:1.0 and an average particle size of 0.1-5.0 mm.Additionally, at least 75 mol % of the C₄-C₆ olefin present is convertedto ethylene, propylene, and/or butylene.

In one embodiment, at least 85 mol % of the C₄-C₆ olefin present isconverted to ethylene, propylene, and/or butylene.

In one embodiment, the C₄-C₆ olefin is 1-hexene, and a mole percentageof propylene produced with respect to moles 1-hexene consumed is 60-85%.

In one embodiment, the C₄-C₆ olefin is 1-hexene, and over a reactionperiod of 24-72 hours, at least 85 mol % of the 1-hexene present isconverted to ethylene, propylene, and/or butylene, and a mole percentageof propylene produced with respect to moles 1-hexene converted is60-85%.

In one embodiment, the C₄-C₆ olefin is present in the gas stream at apartial pressure of 20-500 kPa.

In one embodiment, the gas stream further comprises an inert carriergas.

In one embodiment, the fluoride functionalized zeolite catalyst issubstantially free of phosphorous and sodium.

In one embodiment, the C₄-C₆ olefin is fed to a fixed bed reactor at aflow rate of 5-20 mL/h per g fluoride functionalized zeolite catalyst.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a graph showing an exit gas yield and reactant conversion fora fluoride functionalized zeolite catalyst having a F/Si ratio=2 over a1-hexene stream for 50 hours.

FIG. 2 shows the NH₃-TPD profiles of fluoride functionalized zeolitecatalysts.

FIG. 3 shows water adsorption isotherms of fluoride functionalizedzeolite catalysts.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all embodiments of the disclosure are shown.

The present disclosure will be better understood with reference to thefollowing definitions. As used herein, the words “a” and “an” and thelike carry the meaning of “one or more.” Within the description of thisdisclosure, where a numerical limit or range is stated, the endpointsare included unless stated otherwise.

As used herein, the words “about,” “approximately,” or “substantiallysimilar” may be used when describing magnitude and/or position toindicate that the value and/or position described is within a reasonableexpected range of values and/or positions. For example, a numeric valuemay have a value that is +/−0.1% of the stated value (or range ofvalues), +/−1% of the stated value (or range of values), +/−2% of thestated value (or range of values), +/−5% of the stated value (or rangeof values), +/−10% of the stated value (or range of values), +/−15% ofthe stated value (or range of values), or +/−20% of the stated value (orrange of values). Within the description of this disclosure, where anumerical limit or range is stated, the endpoints are included unlessstated otherwise. Also, all values and subranges within a numericallimit or range are specifically included as if explicitly written out.

As used herein, “compound” is intended to refer to a chemical entity,whether as a solid, liquid, or gas, and whether in a crude mixture orisolated and purified.

As used herein, “composite” refers to a combination of two or moredistinct constituent materials into one. The individual components, onan atomic level, remain separate and distinct within the finishedstructure. The materials may have different physical or chemicalproperties, that when combined, produce a material with characteristicsdifferent from the original components. In some embodiments, a compositemay have at least two constituent materials that comprise the sameempirical formula but are distinguished by different densities, crystalphases, or a lack of a crystal phase (i.e. an amorphous phase).

The present disclosure is intended to include all hydration states of agiven compound or formula, unless otherwise noted or when heating amaterial. For example, aluminum sulfate, Al₂(SO₄)₃, includes anhydrousAl₂(SO₄)₃, Al₂(SO₄)₃.18H₂O, and any other hydrated forms or mixtures.

In addition, the present disclosure is intended to include all isotopesof atoms occurring in the present compounds and complexes. Isotopesinclude those atoms having the same atomic number but different massnumbers. By way of general example, and without limitation, isotopes ofhydrogen include deuterium and tritium. Isotopes of carbon include ¹³Cand ¹⁴C. Isotopes of nitrogen include ¹⁴N and ¹⁵N. Isotopes of oxygeninclude ¹⁶O, ¹⁷O, and ¹⁸O. Isotopes of silicon include ²⁸Si, ²⁹Si, and³⁰Si. Isotopically-labeled compounds of the disclosure may generally beprepared by conventional techniques known to those skilled in the art orby processes analogous to those described herein, using an appropriateisotopically-labeled reagent in place of the non-labeled reagentotherwise employed.

For purposes of the present invention, the Si/Al ratio refers to theSi/Al atomic ratio of the overall crystalline zeolite material and notjust the MFI framework.

According to a first aspect, the present disclosure relates to a methodfor producing a fluoride functionalized zeolite catalyst. Zeolites areporous aluminosilicate minerals that may be found in nature orsynthesized. Elementary building units of zeolites are SiO₄ and AlO₄tetrahedra. Adjacent tetrahedra are linked at their corners via a commonoxygen atom, which results in an inorganic macromolecule with athree-dimensional framework. The three-dimensional framework of azeolite also comprises channels, channel intersections, and/or cageshaving dimensions in the range of 0.1-10 nm, preferably 0.2-5 nm, morepreferably 0.2-2 nm. Water molecules may be present inside thesechannels, channel intersections, and/or cages.

In one embodiment, the fluoride functionalized zeolite catalyst of thepresent disclosure may have a zeolite framework of, or similar to,amicite, ammonioleucite, analcime, barrerite, brewsterite, bellbergite,bikitaite, boggsite, chabazite, chiavennite, clinoptilolite, cowlesite,dachiardite, edingtonite, epistilbite, erionite, faujasite, ferrierite,garronite, gaultite, gismondine, gmelinite, gobbinsite, gonnardite,goosecreekite, gottardiite, harmotome, heulandite, hsianghualite,kalborsite, laumontite, leucite, lévyne, lovdarite, marciopaite,mazzite, merlinoite, mesolite, montesommaite, mordenite, mutinaite,nabesite, natrolite, offretite, pahasapaite, paranatrolite, parthéite,paulingite, perlialite, phillipsite, pollucite, roggianite, scolecite,stellerite, stilbite, terranovaite, tetranatrolite, thomsonite,tschernichite, tschortnerite, tvedalite, wairakite, weinebeneite,willhendersonite, yugawaralite, and combinations thereof. In anotherembodiment, the fluoride functionalized zeolite catalyst may have azeolite framework similar to a synthetic crystalline aluminosilicate,such as zeolites having the trademarked names of ZEOLITE A, ZEOLITE X,ZEOLITE Y, ZEOLITE K-G, ZEOLITE ZK5, ZEOLITE BETA, ZEOLITE ZK-4, SAPO,ALPO, USY, ZEOLITE ZSM-5 (“ZEOLITES SOCONY MOBIL-5” also called moresimply, ZSM-5), ZSM-11, ZSM-12, ZSM-20, ZSM-23, ZSM-35, ZSM-38, ZSM-50,and combinations thereof. Preferably, the fluoride functionalizedzeolite catalyst has a zeolite ZSM-5 framework. In a preferredembodiment, the fluoride functionalized zeolite catalyst is a ZSM-5 typezeolite. In an alternative embodiment, some other catalyst may be usedthat is not a zeolite, such as amorphous silica-alumina.

ZSM-5 type zeolites are composed of several pentasil units linkedtogether by oxygen bridges to form pentasil chains. ZSM-5 type zeolitesmay also be considered as having an MFI framework type. A pentasil unitconsists of eight five-membered rings. In these rings, the vertices areAl or Si and an O is assumed to be bonded between the vertices. Thepentasil chains are interconnected by oxygen bridges to form corrugatedsheets with 10-ring holes. Like the pentasil units, each 10-ring holehas Al or Si as vertices with an O assumed to be bonded between eachvertex. Each corrugated sheet is connected by oxygen bridges to form astructure with straight 10-ring channels running parallel to thecorrugations and sinusoidal 10-ring channels perpendicular to thesheets. Adjacent layers of the sheets are related by an inversion point.The estimated pore size of the channel running parallel with thecorrugations is 5.4-5.6 Å. The crystallographic unit cell of ZSM-5 has96 T sites (Si or Al, the zeolite being based on TO₄ tetrahedrageometry), 192 O sites, and a number of compensating cations dependingon the Si/Al ratio, which ranges from 12 to infinity. The structure isorthorhombic (space group Pnma) at high temperatures, but a phasetransition to the monoclinic space group P2₁/n.1.13 occurs upon coolingbelow a transition temperature between 300 and 350 K.

ZSM-5 type zeolites have a high ratio of silicon to aluminum. Wheneveran Al³⁺ cation replaces a Si⁴⁺ cation, an additional positive charge isrequired to keep the material charge-neutral. With a proton (H⁺) as thecation, the material becomes very acidic. Thus, the acidity isproportional to the Al content. The very regular 3-D structure and theacidity of ZSM-5 type zeolites may be utilized for acid-catalyzedreactions such as hydrocarbon isomerization, cracking, and alkylation.The pore sizes of ZSM-5 type zeolites may be used to impartsize-selectivity into the catalytic reactions. ZSM-5 type zeolites mayalso be used as a support material for catalysis, for example, by beingcoated or decorated with one or more catalytically active metals.

ZSM-5 zeolites may be used either in the alkali metal form, e.g., thesodium form, the ammonium form, the hydrogen form, or another univalentor multivalent cationic form. Preferably, the hydrogen form (acidicform) is employed. They may also be used in intimate combination with ahydrogenating component such as tungsten, vanadium, molybdenum, rhenium,nickel, cobalt, chromium, manganese, or a noble metal such as platinumor palladium where a hydrogenation dehydrogenation function is to beperformed. Such component may be exchanged into the composition,impregnated therein, or physically intimately admixed therewith. Suchcomponent may be impregnated in or on to ZSM-5 such as, for example, by,in the case of platinum, treating the zeolite with a platinummetal-containing ion. Thus, suitable platinum compounds includechloroplatinic acid, platinous chloride, and various compoundscontaining a platinum amine complex.

In a preferred embodiment, the fluoride functionalized zeolite catalystis in an acidic form, which protonates light olefin compounds. Thisinitiates acid-catalyzed reactions, especially hydrocarbon cracking. Theacidity or number of acid sites of the fluoride functionalized zeolitecatalyst may be measured by a liquid phase ion exchange method, agas-phase temperature programmed desorption method, or some othermethod. In one embodiment, a liquid phase ion exchange/filtratetitration method is used to determine an acidity of the fluoridefunctionalized zeolite catalyst. In this method the fluoridefunctionalized zeolite catalyst is first calcined in air and thensubjected to an ion exchange treatment in the presence of an aqueoussodium chloride solution. After the treatment, the solution is filteredto obtain a filtrate. The filtrate is washed with pure/deionized water,and the whole amount of the washing liquid is collected and furthermixed with the aforementioned filtrate. The acidity of the resultingmixed solution (i.e. filtrate+washing liquid) is measured byneutralization titration, and a moles acid per gram of the fluoridefunctionalized zeolite catalyst is reported as the acidity of thezeolite. Alternatively, in a preferred embodiment, an ammoniatemperature-programmed desorption (NH₃-TPD) method is used to measure anacidity of the fluoride functionalized zeolite catalyst. Here, apredetermined amount of the fluoride functionalized zeolite catalyst maybe pretreated at 500° C. in the presence of helium for at least 60minutes, preferably 90 minutes. Then, the fluoride functionalizedzeolite catalyst may be treated at 100° C. in an atmosphere containinghelium and 5-15 vol %, preferably 5-10 vol % of ammonia. After that, thefluoride functionalized zeolite catalyst is heated at a temperatureramping rate of 10° C./min from 100° C. to 600° C., wherein ammonia isdesorbed, and the amount of desorbed ammonia (measured by athermogravimetric analyzer) is used to determine the acidity of thefluoride functionalized zeolite catalyst.

In one embodiment, the fluoride functionalized zeolite catalyst has atotal acidity of 0.017-0.020 mmol/g, preferably 0.017-0.020 mmol/g, morepreferably 0.017-0.020 mmol/g as defined by NH₃-TPD, though in someembodiments, the fluoride functionalized zeolite catalyst may have atotal acidity of less than 0.017 mmol/g or greater than 0.020 mmol/g.Preferably the total acidity, or the number of acid sites per gramcatalyst, is considered equivalent to the number of ammonia moleculesper gram catalyst that desorb.

In one embodiment, the ammonia may desorb in two populations as thefluoride functionalized zeolite catalyst is heated, due to the differentstrengths, availabilities, or geometries of the acid binding siteswithin the zeolite structure. One population may desorb at a temperatureof 80-260° C., preferably 90-240° C., and another population may desorbat a temperature of 260-550° C., preferably 270-480° C. At the lowertemperature range, weakly bounded ammonia may be desorbed at an amountof 0.0040-0.0120 mmol/g, preferably 0.0060-0.0110 mmol/g, morepreferably 0.0080-0.0100 mmol/g, though in some embodiments, less than0.0040 mmol/g or greater than 0.0120 mmol/g may desorb from the zeolite.At the higher temperature range, 0.0080-0.0120 mmol/g, preferably0.0082-0.0115 mmol/g, more preferably 0.0085-0.0197 mmol/g may desorb,though desorption of less than 0.0080 mmol/g or greater than 0.0120mmol/g may be possible in other embodiments.

In one embodiment, the fluoride functionalized zeolite catalyst has asurface area of 330-400 m²/g, preferably 350-380 m²/g, more preferably355-365 m²/g, though in some embodiments, the fluoride functionalizedzeolite catalyst may have a surface area of less than 330-400 m²/g orgreater than 400 m²/g. In a preferred embodiment, the fluoridefunctionalized zeolite catalyst is porous, with a total pore volume of0.15-0.21 cm³/g, preferably 0.16-0.20 cm³/g, more preferably 0.17-0.19cm³/g. However, in some embodiments, the fluoride functionalized zeolitecatalyst may have a total pore volume of less than 0.15 cm³/g or greaterthan 0.21 cm³/g.

In one embodiment, the high surface area and porosity of the fluoridefunctionalized zeolite catalyst may be contributed by both micro-poresand meso-pores. In one embodiment, the fluoride functionalized zeolitecatalyst may have micro-pores (i.e. pores with an average pore diameterof less than 2 nm) having a specific pore volume in the range of 0.1-0.3cm³/g, preferably 0.1-0.2 cm³/g, more preferably 0.15-0.2 cm³/g.Preferably, an average pore diameter of the fluoride functionalizedzeolite catalyst is within the range of 4-12 Å, preferably 5-8 Å, morepreferably 5-6.5 Å. The fluoride functionalized zeolite catalyst mayfurther include meso-pores (i.e. pores with an average pore diameters inthe range of 2-50 nm, preferably 2-20 nm) having a specific pore volumein the range of 0.01-0.15 cm³/g, preferably 0.05-0.15 cm³/g, morepreferably 0.05-0.1 cm³/g. In one embodiment, a specific surface area ofthe micro-pores in the fluoride functionalized zeolite catalyst is inthe range of 100-500 m²/g, preferably 300-500 m²/g, more preferablyabout 400 m²/g, whereas a specific surface area of the meso-pores in thefluoride functionalized zeolite catalyst is in the range of 50-150 m²/g,preferably 50-100 m²/g, more preferably about 80 m²/g. The fluoridefunctionalized zeolite catalyst may be in the form of pellets having adiameter in the range of 0.5-5 mm, preferably 0.5-1.5 mm, morepreferably about 1 mm. The fluoride functionalized zeolite catalyst maybe extrudated to have a geometry selected from the group consisting ofcylindrical, rectilinear, star-shaped, conical, pyramidal, rectangular,cubical, and ring-shaped.

As mentioned earlier, a first aspect of the present disclosure relatesto a method for producing a fluoride functionalized zeolite catalyst.The method involves the step of mixing a structure directing agent, aninorganic fluoride salt, an aluminum salt, a silicating agent, and waterto form a gel. The gel is heated to produce a crystallized product, andthen calcined in air to produce the fluoride functionalized zeolitecatalyst.

In a preferred embodiment, the structure directing agent, the inorganicfluoride salt, the aluminum salt, and water are mixed to form an aqueoussolution, and then the silicating agent is mixed with the aqueoussolution to form the gel. In other embodiments, the components of thegel may be mixed in different orders. Preferably, the components aremixed to form a homogeneous gel. As defined here, a gel is a non-fluidcolloidal network or polymer network that is expanded throughout itswhole volume by a fluid. A gel may be thought of as a solid jelly-likematerial comprised of a substantially dilute cross-linked system, whichexhibits no flow when in the steady-state. By weight, gels are mostlyliquid, and in this way gels are a dispersion of molecules of a liquidwithin a solid. In an alternative embodiment, the fluoridefunctionalized zeolite catalyst may be made from a mixture without themixture forming a gel.

In one embodiment, the gel may comprise the structure directing agent ata weight percentage of 1-10 wt %, preferably 2-7 wt %, more preferably3.5-5.5 wt %, relative to a total weight of the gel However, in someembodiments, the gel may comprise the structure directing agent at aweight percentage lower than 1 wt % or greater than 10 wt %.

In one embodiment, the gel may comprise the inorganic fluoride salt at aweight percentage of 0.1-2.0 wt %, preferably 0.4-1.5 wt %, morepreferably 0.6-1.0 wt %, relative to a total weight of the gel. However,in some embodiments, the gel may comprise the inorganic fluoride salt ata weight percentage of less than 0.1 wt % or greater than 2.0 wt %.

In one embodiment, the gel may comprise the aluminum salt at a weightpercentage of 0.01-1.00 wt %, preferably 0.05-0.50 wt %, more preferably0.06-0.10 wt %, relative to a total weight of the gel. However, in someembodiments, the gel may comprise the aluminum salt at a weightpercentage of less than 0.01 wt %, or greater than 1.00 wt %.

In one embodiment, the gel may comprise the silicating agent at a weightpercentage of 10-17 wt %, preferably 11-15 wt %, more preferably 12-14wt %, relative to a total weight of the gel. However, in someembodiments, the gel may comprise the silicating agent at a weightpercentage of less than 10 wt % or greater than 17 wt %.

In one embodiment, the gel may comprise water at a weight percentage of70-90 wt %, preferably 72-88 wt %, more preferably 75-85 wt %, relativeto a total weight of the gel. However, in some embodiments, the gel maycomprise water at a weight percentage of less than 70 wt % or greaterthan 90 wt %.

In one embodiment, the gel has a F to Si molar ratio of 0.1:1.0-3.0:1.0,preferably 0.5:1.0-2.5:1.0, more preferably 1.5:1.0-2.1:1.0, or about2.0:1.0. In other embodiments, the gel may have a F to Si molar ratio ofless than 0.1:1.0 or greater than 3.0:1.0. In one embodiment, thefluoride functionalized zeolite catalyst may have a F to Si molar ratioof those ranges just discussed for the gel.

In one embodiment, a relative molar composition of the gel may be 1 Si:(0.05-0.12) structure directing agent: (0.0001-0.0030) Al: (0.1-3.0) F:(10-40) H₂O. In another embodiment, a relative molar composition of thegel may be about 1 SiO₂: (0.06-0.10) TPABr: (0.0001-0.0015) Al₂O₃:(0.2-2.5) NH₄F: (15-35) H₂O. In a preferred embodiment, a relative molarcomposition of the gel may be about 1 SiO₂: 0.08 TPABr: 0.0005 Al₂O₃:(0.5-2.0) NH₄F: 20 H₂O.

In one embodiment, the structure directing agent is a quaternaryammonium salt with a chemical formula N(C_(n)H_(3n))₄ ⁺X⁻. X is a halideion or a hydroxide, and n is an integer from 1 to 5. Exemplary halideions include but are not limited to, fluoride, chloride, bromide, andiodide. Accordingly, exemplary structure directing agents include butare not limited to tetramethylammonium hydroxide, tetraethylammoniumhydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide,tetrapentylammonium hydroxide, tetramethylammonium fluoride,tetraethylammonium fluoride, tetrapropylammonium fluoride,tetrabutylammonium fluoride, tetrapentylammonium fluoride,tetramethylammonium chloride, tetraethylammonium chloride,tetrapropylammonium chloride, tetrabutylammonium chloride,tetrapentylammonium chloride, tetramethylammonium bromide,tetraethylammonium bromide, tetrapropylammonium bromide,tetrabutylammonium bromide, tetrapentylammonium bromide,tetramethylammonium iodide, tetraethylammonium iodide,tetrapropylammonium iodide, tetrabutylammonium iodide,tetrapentylammonium iodide. In a preferred embodiment, the halide ion isbromide, and the structure directing agent is tetrapropylammoniumbromide (TPABr). In an alternative embodiment, the structure directingagent is cetyltrimethylammonium chloride, cetyltrimethylammoniumbromide, cetyltrimethylammonium iodide, cetyltriethylammonium bromide,cetyltriethylammonium chloride, cetyltriethylammonium iodide, or anycombination thereof.

The term “inorganic fluoride salt” refers to a chemical compoundconsisting of an inorganic cation and a fluoride anion. Preferably theinorganic fluoride salt is ammonium fluoride (NH₄F) and/or ammoniumbifluoride (NH₄HF₂). In one embodiment, the inorganic fluoride salt isammonium fluoride (NH₄F). In an alternative embodiment, the inorganicfluoride salt may be NaF, CaF₂, KF, HF, MgF₂, LiF, Na₃AlF₆, AlF₃,Na₂SiF₆, boron trifluoride, ammonium fluoborate, ammonium fluosilicate,or some other salt. In another alternative embodiment, an organicfluoride salt may be used instead of an inorganic fluoride salt. Theorganic fluoride salt may be tetramethylammonium fluoride,tetraethylammonium fluoride, tetrapropylammonium fluoride,tetrabutylammonium fluoride, or some other organic fluoride salt. Inanother embodiment, a single compound comprising fluoride, such astetrapropylammonium fluoride, may be used both in place of the inorganicfluoride salt and as the structure directing agent.

In an alternative embodiment, sodium hydroxide may be utilized as areplacement for the fluoride salt. Alternatively, sodium hydroxide mayalso be used in combination with ammonium fluoride (NH₄F) and/orammonium bifluoride (NH₄HF₂).

In one embodiment, the gel and the fluoride functionalized zeolitecatalyst are substantially free of phosphorous and sodium. As definedhere, the gel and the fluoride functionalized zeolite catalyst beingsubstantially free of phosphorous and sodium means that the gel and thefluoride functionalized zeolite catalyst each comprises less than 0.1 wt%, preferably less than 0.01 wt %, more preferably less than 0.005 wt %sodium and phosphorous per relative to a total weight of the gel or thefluoride functionalized zeolite catalyst. In an alternative embodiment,the gel or the fluoride functionalized zeolite catalyst may comprisesodium and/or phosphorous at 0.2-1 wt %, 1-5 wt %, or 5-10 wt % relativeto a total weight of the gel or the fluoride functionalized zeolitecatalyst. In this alternative embodiment, a compound comprising sodiumand/or a compound comprising potassium may be added during the mixing ofthe gel, or after the mixing of the gel; during the synthesis of thefluoride functionalized zeolite catalyst or after the synthesis of thefluoride functionalized zeolite catalyst.

In one embodiment, the aluminum salt is aluminum nitrate or aluminumsulfate. The aluminum salt may be hydrated or anhydrous. Preferably thealuminum salt is hydrated. In other embodiments, the aluminum salt maybe aluminum oxide, aluminum isopropoxide, aluminum borohydride, aluminumacetate, or some other aluminum salt.

In one embodiment, the fluoride functionalized zeolite catalyst has a Sito Al molar ratio of 500:1-2,000:1, preferably 750:1-1,500:1, morepreferably 900:1-1,300:1, or 1,000:1-1,200:1. However, in someembodiments, the fluoride functionalized zeolite catalyst may have a Sito Al molar ratio of less than 500:1 or greater than 2,000:1.

In one embodiment, the fluoride functionalized zeolite catalyst has anaverage crystal size of 0.1-50 μm, preferably 1-40 μm, more preferably5-30 μm, though in some embodiments, the fluoride functionalized zeolitecatalyst may have an average crystal size of smaller than 0.1 μm orgreater than 50 μm. In one embodiment, a plurality of crystals may beagglomerated or aggregated into larger particles, for instance,particles having an average particle diameter of 0.1-5.0 mm, preferably0.2-2.5 mm, more preferably 0.4-1.2 mm. In other embodiments, thecrystals of the zeolite catalyst may be agglomerated or aggregated intoparticles having an average particle diameter of less than 0.1 mm orgreater than 5.0 mm.

In one embodiment, the silicating agent is at least one selected fromthe group consisting of tetraethylorthosilicate (TEOS),tetramethylorthosilicate (TMOS), silica (SiO₂), and polydimethylsiloxane(PDMS). Preferably, the silicating agent is silica, and may be in theform of fused quartz, fumed silica, silica gel, precipitated silica,amorphous silica, mesoporous silica, or aerogel. Preferably the silicais in the form of fumed silica. Fumed silica, also known as pyrogenicsilica, comprises microscopic droplets of amorphous silica fused intobranched, chainlike, three-dimensional secondary particles which thenagglomerate into tertiary particles. Fumed silica generally has a lowbulk density of about 160-190 kg/m³, and a high surface area of about50-600 m²/g. In alternative embodiments, silicate, sodium silicate,tetramethylammonium silicate, and/or sodium metasilicate may be utilizedin conjunction as the silicating agent or in conjunction with asilicating agent previously mentioned.

The water may be tap water, distilled water, bidistilled water,deionized water, deionized distilled water, reverse osmosis water,and/or some other water. In one embodiment the water is bidistilled toeliminate trace metals. Preferably the water is bidistilled, deionized,deionized distilled, or reverse osmosis water and at 25° C. has aconductivity at less than 10 μS·cm⁻¹, preferably less than 1 μS·cm⁻¹; aresistivity greater than 0.1 MΩ·cm, preferably greater than 1 MΩ·cm,more preferably greater than 10 MΩ·cm; a total solid concentration lessthan 5 mg/kg, preferably less than 1 mg/kg; and a total organic carbonconcentration less than 1000 μg/L, preferably less than 200 μg/L, morepreferably less than 50 μg/L.

After mixing to form the gel, the gel may be heated at 180-250° C.,preferably 190-230° C., more preferably 195-210° C. for 12-72 h,preferably 24-56 h, more preferably 36-50 h to produce a crystallizedproduct. Preferably the gel may be heated at pressures higher than 1atm, for instance, 5-35 atm, or 10-20 atm, and may be heated in anautoclave. However, in other embodiments, the gel may be heated at atemperature lower than 180° C. or greater than 250° C. and/or for a timeshorter than 12 h or longer than 72 h. In a preferred embodiment, thegel may be heated at about 200° C. for about 2 days. This heating stepmay be considered as subjecting the gel to a hydrothermalcrystallization process.

The crystallized product may be washed with water and/or an organicsolvent such as acetone, methanol, ethanol, or isopropanol. Acrystallized product that was washed may then be dried in an oven at50-120° C., preferably 60-100° C., more preferably 70-90° C. for 6-24 h,preferably 12-18 h, though in some embodiments, the crystallized productmay be dried at a temperature of lower than 50° C. or greater than 120°C., and/or shorter than 6 h or longer than 24 h.

The crystallized product may be calcined by heating in air at 600-850°C., preferably 675-825° C., more preferably 725-775° C. for 3-12 h,preferably 4-10 h, more preferably 5-7 h to produce the fluoridefunctionalized zeolite catalyst. In other embodiments, the crystallizedproduct may be calcined by heating in air at a temperature of lower than600° C. or higher than 850° C., and/or for a time shorter than 3 h orlonger than 12 h. In one embodiment, the crystallized product may becalcined in an environment other than air, for instance, oxygen-enrichedair. In another embodiment, a crystallized product that was washed maybe dried and consecutively calcined in the same oven or heating device.Preferably the crystallized product is not placed immediately in an ovenor furnace at the calcination temperature, but instead heated graduallyto the calcination temperature, for instance, at a heating rate of 1-7°C./min, preferably 3-5° C./min. Preferably, following the calcination,the fluoride functionalized zeolite catalyst is allowed to graduallycool in order to avoid sudden temperature changes. According to a secondaspect, the present disclosure relates to a fluoride functionalizedzeolite catalyst produced by the method discussed above.

According to a third aspect, the present disclosure relates to a methodof using a fluoride functionalized zeolite catalyst to convert a C₄-C₆olefin into ethylene, propylene, and/or butylene. The method involvescontacting a gas stream of the C₄-C₆ olefin with the fluoridefunctionalized zeolite catalyst at a temperature of 400-700° C. toproduce ethylene, propylene, and/or butylene. Here, the fluoridefunctionalized zeolite catalyst has a F to Si molar ratio of0.1:1.0-3.0:1.0 and an average particle size of 0.1-5.0 mm.Additionally, at least 75 mol % of the C₄-C₆ olefin present is convertedto ethylene, propylene, and/or butylene.

In one embodiment, the gas stream of the C₄-C₆ olefin may be a low valuerefinery or petrochemical hydrocarbon feed stream, such as steam crackerby-products rich in C₄'s and pygas, which otherwise have poor propyleneselectivity when recycled to a steam cracker. In one embodiment, the gasstream of the C₄-C₆ olefin comprises 30-95 wt %, preferably 40-85 wt %of one or more alkenes having 4 to 6 carbon atoms. The term “olefin” asused herein refers to unsaturated straight-chain hydrocarbons,unsaturated branched hydrocarbons, or cyclic unsaturated hydrocarbons.In one embodiment, the C₄-C₆ olefin is selected from the groupconsisting of isomers of butene, isomers of pentene, and/or isomers ofhexene. In one embodiment, the C₄-C₆ olefin is selected from the groupconsisting of 1-butene, cis- and trans-2-butene, butadiene, pentene,pentadiene, hexene, and benzene. In another embodiment, the C₄-C₆ olefinis 1-butene, 1-pentene, and/or 1-hexene. In a preferred embodiment, theC₄-C₆ olefin is 1-hexene.

In another embodiment, the gas stream may comprise hydrocarbons that arenot C₄-C₆ olefins. For instance, in one alternative embodiment, the gasstream may comprise olefins having 7 or more carbon atoms. In anotheralternative embodiment, the gas stream may comprise one or morealiphatic hydrocarbons having 3-10, or 4-8 carbon atoms. Thehydrocarbons may be straight chain, open chain, or cyclic, and may besaturated or unsaturated. Such hydrocarbons may include n-butane,n-butenes, isobutane, isobutene, straight chain, branched chain andcyclic, pentanes, pentenes, hexanes, hexenes, heptanes, heptenes,toluene, propane, propylene, xylene, and ethylbenzene. In otherembodiments, the gas stream of the present invention may include lightnaphthas or raffinates, containing sufficient amounts of C₄-C₇ olefinsand/or paraffins, C₄-C₇ cuts from light naphthas or raffinates,catalytically cracked naphtha, coker naphtha, steam, steam crackerpyrolysis gasoline, synthetic chemical streams containing sufficientamounts of C₄-C₇ olefins and/or paraffins or any other hydrocarbonscontaining sufficient amounts of C₄-C₇ olefins and/or paraffins. Gasstreams comprising high levels of dienes, sulfur, nitrogen, andoxygenates are preferably selectively hydrotreated prior to contactingwith the fluoride functionalized zeolite catalyst. However, certain gasstreams with low levels of dienes, sulfur, nitrogen, metal compounds,and oxygenates may be processed directly from FCC units, cokers, orsteam crackers without any pretreatment.

As mentioned earlier, at least 75 mol % of the C₄-C₆ olefin present isconverted to ethylene, propylene, and/or butylene, relative to the totalmoles of C₄-C₆ olefin initially present. In other words, the conversionof the C₄-C₆ olefin is at least 75%. In another embodiment, theconversion of the C₄-C₆ olefin is at least 80%, preferably at least 85%,more preferably at least 90%, even more preferably at least 95%, thoughin some embodiments, the conversion may be lower than 75%. In onepreferred embodiment, at least 85 mol % of the C₄-C₆ olefin present isconverted to ethylene, propylene, and/or butylene.

In one embodiment, the C₄-C₆ olefin may be converted to a mixture ofethylene, propylene, and/or butylene. For instance, relative to thetotal weight of the C₄-C₆ olefin converted, 1-15 wt %, preferably 2-10wt % may be converted to ethylene; 5-25 wt %, preferably 10-20 wt % maybe converted to butylene, and 60-85 wt %, preferably 62-75 wt % may beconverted to propylene. Other products such as hydrogen gas, pentene,and methane may also be produced.

In one embodiment, the C₄-C₆ olefin is 1-hexene, and a mole percentageof propylene produced with respect to moles 1-hexene consumed is 60-85%,preferably 62-82%, more preferably 65-80%. This mole percentage may beconsidered as the selectivity of propylene. In other embodiments,however, the C₄-C₆ olefin may be 1-hexene while the selectivity ofpropylene is lower than 60% or greater than 85%. In one embodiment, theselectivity of propylene may be increased over different fluoridefunctionalized zeolite catalysts as the F/Si ratio is increased. In analternative embodiment, the selectivity of propylene may be tuned bychanging the pore size of a zeolite catalyst, or by functionalizing afluoride functionalized zeolite catalyst or some other zeolite catalystwith different chemical groups.

A yield of a product may be determined by multiplying the conversionpercentage of the reactant (here, the C₄-C₆ olefin), with theselectivity of the product. In one embodiment, a product is propylene,and is produced with a yield of 60-95%, preferably 62-90%, morepreferably 65-80%. However, in some embodiments, propylene may beproduced with a yield of lower than 60% or greater than 95%.

In one embodiment, the C₄-C₆ olefin is present in the gas stream at apartial pressure of 20-500 kPa, preferably 30-400 kPa, more preferably35-345 kPa, even more preferably 50-300 kPa. However, in someembodiments, the C₄-C₆ olefin may be present in the gas stream at apartial pressure of less than 20 kPa or greater than 500 kPa. In oneembodiment, the total pressure of the gas stream may be 50-600 kPa,preferably 100-500 kPa, more preferably 100-400 kPa, even morepreferably 100-300 kPa, though in other embodiments, the total pressureof the gas stream may be lower than 50 kPa or greater than 600 kPa. Inone embodiment, the total pressure of the gas stream may be aboutatmospheric pressure, or about 101 kPa. In one embodiment, the C₄-C₆olefin may be present at a partial pressure that changes throughout thecourse of the catalytic reaction.

In one embodiment, the gas stream comprises an inert carrier gas. Theinert carrier gas may be helium, nitrogen, argon, or some other inertgas. Preferably the inert carrier gas is nitrogen. In other embodiments,the gas stream may comprise a carrier gas that is not considered aninert gas, such as air, steam, or carbon dioxide.

In one embodiment, the fluoride functionalized zeolite catalyst issubstantially free of phosphorous and sodium. As defined here, thefluoride functionalized zeolite catalyst being substantially free ofphosphorous and sodium means that the fluoride functionalized zeolitecatalyst comprises less than 0.1 wt %, preferably less than 0.01 wt %,more preferably less than 0.005 wt % sodium and phosphorous relative toa total weight of the fluoride functionalized zeolite catalyst. In analternative embodiment, the fluoride functionalized zeolite catalyst maycomprise sodium and/or phosphorous at 0.2-1 wt %, 1-5 wt %, or 5-10 wt %relative to a total weight of the fluoride functionalized zeolitecatalyst. In this alternative embodiment, a compound comprising sodiumand/or a compound comprising potassium may be added during the synthesisof the fluoride functionalized zeolite catalyst or after the synthesis.

In one embodiment, the C₄-C₆ olefin is fed to a fixed bed reactor at aflow rate of 5-20 mL/h per g fluoride functionalized zeolite catalyst,preferably 7-18 mL/h per g fluoride functionalized zeolite catalyst,more preferably 9-13 mL/h per g fluoride functionalized zeolitecatalyst. In a preferred embodiment, the C₄-C₆ olefin is fed to a fixedbed reactor at a flow rate of about 12 mL/h per g fluoridefunctionalized zeolite catalyst, though in other embodiments, the C₄-C₆olefin may be fed to the fixed bed reactor at a flow rate of less than 5mL/h per g, or greater than 20 mL/h per g fluoride functionalizedzeolite catalyst.

In one embodiment, the C₄-C₆ olefin may be fed to a reactor with a gashourly space velocity (GHSV) of 400-15,000 hr⁻¹, preferably 800-10,000hr⁻¹, more preferably 1,000-5,000 hr⁻¹, even more preferably 1,200-3,000hr⁻¹. However, in some embodiments, the C₄-C₆ olefin may be fed to areactor with a GHSV of less than 400 hr⁻¹ or greater than 15,000 hr⁻¹.

In one embodiment, the C₄-C₆ olefin may be fed to the fluoridefunctionalized zeolite catalyst at a W/F ratio (catalyst weight/feedflow rate) of 0.05-0.30 h, preferably 0.08-0.25 h, more preferably0.10-0.20 h, or about 0.125 h. However, in other embodiments, the olefinmay be fed to the fluoride functionalized zeolite catalyst at a W/Fratio of less than 0.05 h or greater than 0.30 h.

According to a second aspect of the disclosure, the present disclosurerelates to a fluoride functionalized zeolite catalyst created by themethod of the first aspect of the disclosure.

In one embodiment, the method of the third aspect of the disclosure usesa fluoride functionalized zeolite catalyst created by or substantiallysimilar to the fluoride functionalized zeolite catalyst of the firstaspect of the disclosure.

“Contacting,” as used herein refers to a process whereby avaporized-state of the C₄-C₆ olefin in the gas stream is directlycontacted with the fluoride functionalized zeolite catalyst present in acatalyst bed of a reactor at reaction conditions that are favored forcatalytic reactions to take place. The C₄-C₆ olefin may be contactedwith the catalyst by passing through the catalyst or by passing over thecatalyst (e.g. a vaporized-state of the C₄-C₆ olefin as an atmosphere tothe catalyst). Additionally, the C₄-C₆ olefin may be contacted with thecatalyst by mixing the C₄-C₆ olefin and the fluoride functionalizedzeolite catalyst as a heterogeneous solution. Among these, the preferredcontacting is by passing the gas stream of the C₄-C₆ olefin through thefluoride functionalized zeolite catalyst, for example as a catalyst bed.In other embodiments, the contacting may be accomplished by anyconventional technique, for example, by using the fluoridefunctionalized zeolite catalyst in a fixed bed system, a moving bedsystem, a fluidized bed system, or in a batch type operation. In oneembodiment, the fluoride functionalized zeolite catalyst, as part of acatalyst bed or separate, may be attached or embedded in a support ormatrix material such as silica, alumina, silica-alumina, clay, andmixtures thereof.

The “catalyst bed” as used herein refers to a container with an internalcavity that is filled with the fluoride functionalized zeolite catalyst.Examples of the catalyst beds include, but are not limited to a hollowtube, a pipe, a duct, etc. The reactor may preferably be a cylindricalvessel with the catalyst bed located inside, wherein olefin stream iscontacted with the zeolite catalyst. The reactor may include one or morecatalyst beds that are located in series. In a preferred embodiment, thereactor has only one catalyst bed. The reactor may have variousgeometries including spherical, conical, pyramidal, rectangular, orcubical geometries. In one embodiment, the reactor has a volume of lessthan 1 mL, preferably less than 500 μL. In another embodiment, thereactor has a volume in the range of 1-1,000 mL, preferably 10-1,000 mL,more preferably 10-100 mL. In another embodiment, the reactor has avolume in the range of 1-10,000 L, preferably 100-1,000 L, morepreferably 500-1,000 L. In a preferred embodiment, reaction conditionsare selected such that C₄-C₆ olefins present in the gas stream areconverted to propylene. In alternative embodiments, the catalyticreactions may also include transalkylation, and/or disproportionation ofthe C₄-C₆ olefins. Transalkylation, refers to a chemical reactionthrough which one or more alkyl groups (e.g. methyl, ethyl, propyl,butyl, etc.) are transferred from one organic compound to another.Disproportionation refers to a redox reaction in which an organicmolecule is reduced in a reduction reaction, and the similar organicmolecule is also oxidized in an oxidation reaction, thereby forming twodifferent products.

In one embodiment, both the conversion percentage of a C₄-C₆ olefin,and/or some other hydrocarbon reactant in the gas stream, and theselectivity of one or more products, are sustained for a reaction periodof 10-24 hours, or 12-72 hours, or at least 24 hours, preferably atleast 36 hours, more preferably at least 50 hours. As defined here, aconversion percentage and a selectivity being sustained for a certainreaction period means that for a reaction period, the conversionpercentage and the selectivity each vary by less than 10%, preferablyless than 7%, more preferably less than 5% of each respective mean valueover that period.

In one embodiment, the C₄-C₆ olefin is 1-hexene, and over a reactionperiod of 24-72 hours, preferably 36-60 hours, at least 85 mol %,preferably at least 90 mol %, more preferably at least 95 mol % of the1-hexene present is converted to ethylene, propylene, and/or butylene,and a mole percentage of propylene produced with respect to moles1-hexene converted is 60-85 mol %, preferably 62-80 mol %. In a relatedembodiment, the fluoride functionalized zeolite catalyst is able tosustain both the conversion of 1-hexene and the selectivity of propylenefor at least 24 hours, preferably at least 36 hours, more preferably atleast 50 hours. In other embodiments, the fluoride functionalizedzeolite catalyst is able to sustain both the conversion of 1-hexene andthe selectivity of propylene for at least 60 hours, preferably at least72 hours, more preferably at least 84 hours.

Preferably, the fluoride functionalized zeolite catalyst has highselectivity, and under the conditions of hydrocarbon conversion providesa high percentage of desired products compared to similar zeolitecatalysts that are not fluoride functionalized. In addition, the abilityfor the fluoride functionalized zeolite catalyst to be physically stableunder high temperatures and/or high pressures is important for acracking catalyst. During catalytic conversion, however, the crackingreaction may be accompanied by a number of other side reactions such asaromatization, polymerization, alkylation, isomerization, and the like.

As a result of these side reactions, carbonaceous deposits, referred as“coke,” may be formed on the fluoride functionalized zeolite catalyst.This deposit of coke may impair the catalyst efficiency, decreasing therate of conversion and/or decreasing the selectivity of the products.For instance, in one embodiment, the formation of coke may decrease theconversion percentage of 1-hexene and/or the selectivity of propylene.It may be possible to remove the fluoride functionalized zeolitecatalyst after coke has been deposited thereon and to regenerate it byburning the coke in a stream of oxidizing gas. Alternatively, thefluoride functionalized zeolite catalyst may be regenerated in place,without being removed from a reactor. In one embodiment, the fluoridefunctionalized zeolite catalyst may be regenerated to remove coke byheating in a oxidizing gas stream (for instance, comprising O₂ gas) andat a temperature of 500° C.-900° C., preferably 600° C.-850° C. Theregenerated fluoride functionalized zeolite catalyst may then be reused.

In one embodiment, a weight percentage of coke formed relative to acombined mass of a fluoride functionalized zeolite catalyst with coke islower or divided by a factor of at least 2, preferably at least 2.5,more preferably at least 3.0, even more preferably at least 3.5 comparedto a similar zeolite catalyst, without fluoride functionalization, beingused under the same reaction conditions.

For instance, in one embodiment, the weight percentage of coke formed ona fluoride functionalized zeolite catalyst having a F/Si molar ratio of1.6-2.5, preferably 1.8-2.2, may be 0.20-1.50 wt %, preferably 0.35-1.20wt %, more preferably 0.55-0.95 wt %, relative to a combined mass of thecoke and fluoride functionalized zeolite catalyst, for a reaction periodof 40-60 h, preferably 45-55 h. The weight percentage of coke formed ona substantially similar, yet non-fluoride functionalized zeolitecatalyst, under the same reaction conditions, may be 1.50-6.00 wt %,preferably 1.75-4.00 wt %, more preferably 2.00-3.50 wt % relative to atotal weight of the zeolite catalyst and coke.

The examples below are intended to further illustrate protocols forpreparing, characterizing the fluoride functionalized zeolite catalystand uses thereof, and are not intended to limit the scope of the claims.

Example 1

ZSM-5 Synthesis with Different F/Si Ratio by Hydrothermal Method

The present invention disclosure provides a method for synthesizingactive ZSM-5 catalysts (i.e. fluoride functionalized zeolite catalysts)for cracking of C₄-C₆ olefins to light olefins. The MFI crystalstructure with intersecting 10 membered-ring pore channels having aSiO₂/Al₂O₃ ratio of 2000 were synthesized using different F/Si ratiofrom 0 to 2.0. Physico-chemical characterization of ZSM-5 with F/Siratio of 0, 0.5, 1.0, 1.6, and 2.0 are presented in Table 1. All thecatalyst showing similar very weak acidic sites as expected. However,catalyst B, C and D shows slightly higher than catalyst A and E. Eventhough the acidity of catalyst B, C and D is close, the activity ofcatalyst D was higher as compared to other catalysts. The conversion of1-hexene was above 93% at 450° C. and it further increases with increasein temperature (99% at 600° C.). The yield of light olefins at 550 and600° C. remains the same. At low temperature (450° C.), about 25%butenes formation was observed. In all the cases, a F/Si ratio of 2showed higher activity than the other catalysts, even though the acidityof F/Si=1.0, 1.6, and 2 remains the same. Upon increasing the reactiontemperature from 450 to 500° C., the formation of butenes was reduced to17% at 550° C., and it was further decreased to 12% at 600° C. At thesame time, the yield of ethylene increased as the reaction temperatureincreased. The higher activity catalyst D is related to the amount offluoride ions in the synthesis of ZSM-5. The fluorine atom present inthe zeolite framework creates a more hydrophilic environment in thecatalyst. The hydrophilic nature and weak acid sites are found to beresponsible for higher propylene selectivity.

The operating conditions of the 1-hexene cracking reaction comprisetemperatures between about 350° C. to about 700° C. A preferredtemperature for operating the process is within the range from about400° C. to about 650° C. with a more preferred operating temperature ofabout 450° C. to about 600° C. The reaction process operation conditionsfurther include hydrocarbon partial pressures between about 35 kPa (5psia) to about 345 kPa (50 psia). The catalytic process of 1-hexenecracking may be conducted in a continuous circulating fluidized-bedreactor, a dense fluidized-bed reactor, a fixed-bed reactor, or in afixed-bed swing reactor. The W/F ratio, feed rate of 1-hexene, andcatalyst weight were 0.125 h, 1.8 mL/h, and 0.15 g, respectively.

The present invention is further explained in the following examples,however, this invention is not restricted to these examples.

In a typical synthesis, 4.26 g tetrapropylammonium bromide (TPABr) and0.74 g ammonium fluoride (NH₄F) and 0.0750 g hydrated aluminum nitratewere dissolved into 72 mL of water. Then, 12 g of fumed silica was addedand stirred until a homogeneous gel was formed. The gel was subjected tohydrothermal crystallization process at 200° C. for 2 days. The molarcomposition of the gel was 1 SiO₂: 0.08 TPABr: 0.0005 Al₂O₃: (0.5-2.0)NH₄F: 20 H₂O. The gel was washed with water and dried at 80° C.overnight. The template was removed by calcination at 750° C. for 6 h inair. The synthesized ZSM-5 zeolites with F/Si molar ratios of 0.5, 1.0,1.6 and 2.0 are denoted by F-ZSM-5(A), F-ZSM-5(B), F-ZSM-5(C) andF-ZSM-5(D), respectively.

TABLE 1 Physico-chemical characterization of ZSM-5 with F/Si ratio of 0,0.5, 1.0, 1.6, and 2.0. F/Si Si/Al Surface molar molar area V_(total)NH₃-TPD (mmol/g) sample ratio ratio (m²/g) (cm³/g) LT HT TA ZSM-5(E) 01049 354 0.17 0.0037 0.0070 0.0107 ZSM-5(A) 0.5 1182 374 0.17 0.00380.0073 0.0111 ZSM-5(B) 1.0 1198 379 0.19 0.0091 0.01 0.0191 ZSM-5(C) 1.61222 360 0.17 0.0098 0.0094 0.0192 ZSM-5(D) 2.0 1356 357 0.17 0.00950.0088 0.0183 LT = Low temperature; HT = High temperature; TA = TotalAcidity

Example 2

ZSM-5 Synthesis without Fluoride by Hydrothermal Method

ZSM-5 with Si/Al₂ ratio of 2000 without NH₄F was also synthesized usingthe following procedure. In a typical synthesis, 10.76 g sodium metasilicate and 0.28 g sodium hydroxide in 58.5 g of water was mixed in abeaker (Solution A). 2.36 g of tetrapropyl ammonium bromide in 86 g ofH₂O was mixed with 0.028 g hydrated aluminum sulfate. Then 1.55 gsulfuric acid was added (Solution B). In a separate beaker, 7 g ofsodium hydroxide was dissolved in 137.5 of water (Solution C) andSolution A followed by Solution B was added to this mixture. Theobtained gel was aged for 24 h at constant stirring. The molarcomposition of the gel was 1 SiO₂: 0.1 TPA⁺: 0.0005 Al₂O₃: 1.71 Na₂O:178 H₂O. The mixture obtained was poured into a Teflon-sealed stainlesssteel bottle and heated to 150° C. for 72 h. The precipitate thusobtained was washed with alcohol, dried at 100° C. for 12 h, andcalcined at 550° C. for 5 h in an air stream. Physically adsorbed and/orion-exchanged sodium ions on the zeolite surface were removed andexchanged with NH₄ ⁺ using a conventional ion exchange technique with a10% NH₄NO₃ aqueous solution and calcined at 550° C. for 5 h in an airstream. The synthesized catalyst by this procedure is denoted as ZSM-5(E).

Example 3

Catalytic Performance of Modified ZSM-5 Catalysts

The catalytic performance of the modified ZSM-5 catalysts was evaluatedin a fixed-bed packed with 2 mL of the catalyst with a particle size of0.5-1.0 mm diameter. The catalyst sample was pretreated in a nitrogenstream at 550° C. for 1 h and then a mixture of the 1-hexene (1.8 mL/h)and nitrogen (21 mL/min) (GHSV=900 h⁻¹) was passed through the catalystbed at different temperature from 450 to 600° C. The products wereanalyzed by on-line GC equipped thermal conductivity detector (TCD) anda flame ionization detector (FID).

The results of catalytic performance in 1-hexene butene cracking usingZSM-5 catalysts are presented in Table 2. Catalyst D showed highestpropylene as compared to other catalysts. Propylene yield was increasedwith reaction temperature from 450 to 600° C. as well as with increasein F/Si ratio. Time on stream study was carried out using Catalyst D isshown in FIG. 1. The results show that Catalyst C was stable for 50hours of the 1-hexene stream. The amount of coke formation was found tobe 0.77 wt % for catalyst D after 50 h of stream. For catalyst E, thecoke formation was found to be 2.75 wt % within 5 hours of 1-hexenestream. This clearly indicates that the catalyst synthesized by fluoridemethod show excellent stability as compared without fluoride method.

TABLE 2 Yield of light olefins (C-mol %) in cracking of 1-hexene usingdifferent catalysts at 1 bar, TOS = 1 hr, W/F = 0.125 h. ReactionTemperature 450° C. 500° C. 550° C. 600° C. Catalyst C2═ C3═ C4═ C2═ C3═C4═ C2═ C3═ C4═ C2═ C3═ C4═ ZSM-5(E) 1.61 33.07 12.09 2.76 55.58 9.43.65 67.26 8.36 5.05 57.87 7.89 ZSM-5(A) 2.73 34.98 26.93 4.53 55.0920.9 6 67.89 14.53 7.58 69.3 12.12 ZSM-5(B) 2.92 36.87 27.24 4.53 56.4720.68 6.01 68.38 14.5 7.79 69.39 12.43 ZSM-5(C) 2.68 37.32 25.71 4.257.15 18.69 5.41 68.87 13.32 7.5 68.62 12.02 ZSM-5(D) 2.63 39.34 25.163.93 58.89 17.46 5.12 70.23 12.72 6.58 72.49 11.52

Example 4

Water Adsorption Isotherm of Modified ZSM-5 Catalysts with F/Si Ratiosof 0.5, 1.0, 1.6, and 2.0.

The hydrophilic and hydrophobic properties of the modified ZSM-5catalyst zeolite samples were measured using a water adsorptionmeasurement, and the amount of water adsorbed is shown in FIG. 3. Thewater uptake behavior in FIG. 3 shows an increase in total water uptakecapacity with an increase in the F/Si ratio. The amount of Al content inall the samples remained constant, indicating that the increase in wateruptake is due to the presence of fluoride ions in ZSM-5.

The water adsorption measurements were carried out at 25° C. using aBELSORP MAX (BEL JAPAN Co. Ltd.) at water vapor saturated pressure (3.14kPa at 25° C.). Before this measurement, the sample was degassed at 400°C. for 24 h.

The effect of fluoride ions on ZSM-5 catalyst synthesis and catalyticactivity was studied. ZSM-5 was synthesized by a hydrothermalcrystallization process using tetrapropyl ammonium bromide (TPABr) as astructure directing agent in a fluoride medium. The synthesized catalystwas used to perform a catalytic cracking reaction of 1-hexene in afixed-bed reactor at 450-600° C. under atmospheric pressure. The effectof different ratios of fluoride ions was tested in the catalyticcracking of 1-hexene. The results revealed that ZSM-5 with F/Si ratio of2 showed highest propylene selectivity of 72 wt % with 99% conversion of1-hexene at 600° C. The synthesized ZSM-5 catalyst presented in thisinvention may be used in stand-alone units dedicated for the cracking ofC₄-C₆ olefins, which are produced from FCC crackers or ethylenecrackers. The effect of F/Si ratio was investigated by catalyticcracking of 1-hexene. The present invention produces a higher yield ofpropylene with different P/E ratio. The enhanced propylene selectivityis related to the amount of fluorine atom present in the zeoliteframework, which may create a more hydrophilic environment in thecatalyst. The hydrophilic nature of the catalyst with weak acid sitesmay be responsible for higher propylene selectivity. The catalystlifetime studies showed that the catalyst was stable throughout 50 hoursof exposure to a 1-hexene stream.

The invention claimed is:
 1. A method for producing a fluoridefunctionalized zeolite catalyst, the method comprising: mixing astructure directing agent, an inorganic fluoride salt, an aluminum salt,a silicating agent, and water to form a gel, wherein the gel has a F toSi molar ratio of 1.5:1.0-2.1:1.0; heating the gel at 180-250° C. for12-72 h to produce a crystallized product; and calcining thecrystallized product in air at 600-850° C. for 3-12 h to produce thefluoride functionalized zeolite catalyst, wherein the silicating agentis fumed silica, wherein the gel is formed from components consisting ofthe structure directing agent, the inorganic fluoride salt, the aluminumsalt, the silicating agent, and water, wherein the fluoridefunctionalized zeolite catalyst has an average crystal size of 5-30 μm,wherein the fluoride functionalized zeolite catalyst has a Si to Almolar ratio of 1,000:1-1,200:1, and wherein the gel and the fluoridefunctionalized zeolite catalyst each comprises less than 0.005 wt %phosphorous and sodium relative to a respective total weight.
 2. Themethod of claim 1, wherein the structure directing agent is a quaternaryammonium salt with a chemical formula N(C_(n)H_(3n))₄ ⁺X⁻, with X beinga halide ion or a hydroxide, and n being an integer from 1 to
 5. 3. Themethod of claim 2, wherein the structure directing agent istetrapropylammonium bromide.
 4. The method of claim 1, wherein theinorganic fluoride salt is ammonium fluoride.
 5. The method of claim 1,wherein the aluminum salt is aluminum nitrate or aluminum sulfate. 6.The method of claim 1, wherein the fluoride functionalized zeolitecatalyst has a total acidity of 0.017-0.020 mmol/g as defined byNH₃-TPD.
 7. The method of claim 1, wherein the fluoride functionalizedzeolite catalyst is a ZSM-5 type zeolite.
 8. The method of claim 1,wherein the fluoride functionalized zeolite catalyst has a surface areaof 330-400 m²/g.
 9. The method of claim 1, wherein the gel comprises theinorganic fluoride salt at a weight percentage of 0.6-1.0 wt %, relativeto a total weight of the gel.
 10. A fluoride functionalized zeolitecatalyst, produced by the method of claim 1.